diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index cd1615f..2042b8e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -81,6 +81,12 @@
       - name: Checkout repository from github
         uses: actions/checkout@v4
 
+      - name: Check Filelist (for packaging)
+        run: |
+          # If any files in the repository are not listed in Filelist this will
+          # exit with an error code and list the missing entries.
+          make -f ci/unlisted.make
+
       - run: sudo dpkg --add-architecture i386
         if: matrix.architecture == 'i386'
 
diff --git a/Filelist b/Filelist
index 21abf4b..efb2daa 100644
--- a/Filelist
+++ b/Filelist
@@ -213,6 +213,7 @@
 		src/testdir/dumps/*.dump \
 		src/testdir/dumps/*.vim \
 		src/testdir/samples/*.txt \
+		src/testdir/samples/*.vim \
 		src/testdir/samples/test000 \
 		src/testdir/color_ramp.vim \
 		src/testdir/silent.wav \
@@ -1074,4 +1075,17 @@
 		src/po/*.mo \
 		runtime/lang/Make_mvc.mak \
 
+# Files in the repository that are deliberately not listed above, and will thus
+# be excluded from distribution tarballs and the like.
+# This excludes them from the CI check for unlisted files.
+IGNORE = \
+		.appveyor.yml \
+		.github/FUNDING.yml \
+		.github/labeler.yml \
+		.github/workflows/label.yml \
+		SECURITY.md \
+		ci/unlisted.make \
+		src/libvterm/CODE-MAP \
+		runtime/syntax/testdir/input/html_html \
+
 # vim: set ft=make:
diff --git a/ci/unlisted.make b/ci/unlisted.make
new file mode 100644
index 0000000..04dfcb5
--- /dev/null
+++ b/ci/unlisted.make
@@ -0,0 +1,49 @@
+# vim: ft=make
+SHELL = /bin/bash
+
+# List all files that are tracked in git but not listed in Filelist.
+# Exit code is 2 ("Make encountered an error") if any such files exist.
+
+# Filelist is a Makefile that defines many variables, so we use Make itself to
+# query which variables it defines, then expand them all by wrapping each name
+# in $(...), importing Filelist and using $(eval).
+
+include Filelist
+$(eval all_patterns := $(shell \
+	make -f Filelist --question --print-data-base --no-builtin-rules \
+		--no-builtin-variables 2>/dev/null \
+	| sed -nre \
+		'/^# makefile .from \x27Filelist\x27,/ { \
+			n; \
+			s/ = .*//; \
+			T; \
+			s/.*/$$(\0)/; \
+			p; \
+		}'))
+
+# In Makefile's `prepeare` target, all the IN_README_DIR files are moved from
+# READMEdir to the root, so add those files in their Git-tracked location:
+all_patterns := $(all_patterns) \
+	$(foreach readme, $(IN_README_DIR), READMEdir/$(readme))
+
+# The result 'all_patterns' is a list of patterns (globs), which we expand with
+# wildcard to get actual filenames.  Note this means Filelist can list a file
+# that does not exist, and it will be omitted at this step.
+listed_files := $(wildcard $(all_patterns))
+
+# Default target to actually run the comparison:
+.PHONY: check
+check:
+	@# There are too many files to list on the command line, so we write
+	@# that to a temporary file, one per line.
+	$(file > Filelist-listed-files)
+	$(foreach filename, $(listed_files),\
+		$(file >> Filelist-listed-files,$(filename)))
+	@# Compare the sorted lists.  Delete that temporary file on both
+	@# success and failure, but exit with diff's exit code.
+	diff -u0 --label files-in-git <(git ls-files | sort) \
+		--label Filelist <(sort --unique Filelist-listed-files); \
+	RV=$$?; \
+	rm Filelist-listed-files; \
+	(($$RV != 0)) && echo "Add files to the right variable in Filelist."; \
+	exit $$RV